This invention involves the shaping and bonding of metal assemblies by pressing at high temperatures. More specifically, this invention relates to a press assembly and method of isostatic pressing in a cold chamber.
Hot isostatic pressing, as exemplified by U.S. Pat. No. 3,739,617 to Stejskal, basically involves preparing an assembly of metal parts, powdered metal, etc., on a forming surface, covering the assembly with a flexible blanket or deformable bag and placing the assembly in an autoclave at high temperature and pressure to form and bond the assembly.
This is a very effective manufacturing technique for a variety of materials and assemblies. However, this method is difficult to use with parts that cannot be pressed with a simple bag and is often wasteful of energy where a large autoclave must be heated to press a small volume of assemblies. Complex, flexible, sheet metal housing have been designed for forming and bonding complex shapes by hot isostatic pressing. Typical are those described by Borchert et al in U.S. Pat. No. 4,575,327. These housing and the pressure transmitting components are expensive and difficult to design for proper assembly and disassembly without interference either before and after pressing.
Attempts have been made to use granular materials, such as is shown by Rigby et al in U.S. Pat. No. 4,552,710 or molten glass (Schilling et al, U.S. Pat. No. 4,183,456) as the pressure transmitting medium for complex shapes. Pressure is often not entirely isostatic and removing the material after pressing is often difficult and the material may adversely react with the assembly materials when brought into contact with them at high temperatures.
Expandable bags, as shown, for example by Schwarzkopf in U.S. Pat. No. 3,922,127, and materials with a high coefficient of thermal expansion as taught by Horn et al, U.S. Pat. No. 3,795,559, have been used to apply pressure to complex areas of an assembly. These techniques have been generally limited to low melting metals and low temperature fabrication of fiber reinforced synthetic resin matrix materials.
Therefore, there continues to exist an unmet need for methods and apparatus for forming and/or bonding metal parts at high temperatures which permit the use of complex tooling while having lower heating energy requirements.